New organometallic osmium(VI) complexes with sulfur and oxygen containing ligands, (Os(N)(CH$\sb2$SiMe$\sb3)\sb2$Y) $\sp-$ $\{$Y = (SCH$\sb2$CH$\sb2$S), (SCN)$\sb2$, (S), (S-C$\sb5$H$\sb4$N), (WS$\sb4$), (MoS$\sb4$), (SO$\sb4$), (CO$\sb3$), (ReO$\sb4)\sb2\}$ were prepared. Two crystal structures of (Os(N)(R)$\sb2$(SC$\sb5$H$\sb4$N)) $\sb2$, (NBu$\sp{\rm n}\sb4$) (Os(N)(R)$\sb2$(WS$\sb4$)) (R = CH$\sb2$SiMe$\sb3)$ were determined.The first osmium and ruthenium alkyl complexes containing bidentate chromate group (NBu$\sp{\rm n}\sb4$) (M(N)(CH$\sb2$SiME$\sb3)\sb2$(CrO$\sb4$)) (M = Os, Ru) were synthesized by the reaction of (M(N)R$\sb2$Cl$\sb2$) $\sp-$ with Ag$\sb2$CrO$\sb4$ or K$\sb2$CO$\sb4$ in high yields. A crystal structure of (NBu$\sp{\rm n}\sb4$) (Ru(N)(CH$\sb2$SiMe$\sb3)\sb2$(CrO$\sb4$)) was determined. All of the osmium and ruthenium complexes are thermally stable to air and water and soluble in organic solvents.The osmium and ruthenium chromate complexes, cis- (NBu$\sp{\rm n}\sb4$) (M(N)(CH$\sb2$SiMe$\sb3)\sb2$CrO$\sb4$) (M = Ru, Os) are catalysts for selective oxidation of alcohols to the corresponding carbonyl compounds under mild conditions with molecular oxygen as a secondary oxidant. Kinetic and mechanistic studies were carried out on the oxidation of benzyl alcohol by cis- (NBu$\sp{\rm n}\sb4$) (Os(N)(CH$\sb2$SiMe$\sb3)\sb2$CrO$\sb4$). The reaction is first order in both cis- (NBu$\sp{\rm n}\sb4$) (Os(N)(CH$\sb2$SiMe$\sb3)\sb2$CrO$\sb4$) and O$\sb2$ and zero order in alcohol. Dioxygen labelling studies show that the $\sp{17}$O$\sb2$is incorporated into the bridge oxo of cis- (NBu$\sp{\rm n}\sb4$) (Os(N)(CH$\sb2$SiMe$\sb3)\sb2$CrO$\sb4$). The most likely mechanism for the oxidation of alcohols by cis- (NBu$\sp{\rm n}\sb4$) (Os(N)(CH$\sb2$SiMe$\sb3)\sb2$CrO$\sb4$) involves a concentrated $\beta$-hydrogen elimination and oxygen insertion as a rate-determining step.